Which has more thermal energy given they have the same temperature, a whole apple pie or a piece of apple pie?

Answer: a whole apple pie

Explanation:

The thermal content of a material is the product of its mass times the specific heat capacity times the temperature change.

In this case both samples have the same specific heat capacity (they are made of the same materials), both are at the same temperature. The only difference is their masses, and the full apple pie will have more mass than the apple pie piece, hence, the full apple pie will hold more thermal energy.